Photoaging can be defined as the characteristic changes to skin, induced by chronic UVA (ultraviolet A) and UVB (ultraviolet B) exposure. UVB rays are a primary mutagen that can penetrate through the epidermal layer (the outermost layer) of the skin, resulting in mutations. UVA rays on the other hand can penetrate into deeper layers of the skin. Sun burn, a form of an acute inflammatory response is due to the penetrative nature of UVB, whereas UVA is more responsible for skin ageing. However, it is important to note that both UVA and UVB exposure can cause long term photoageing.Skin types 1&2 (skin prone to burning and rarely tanning) are at the greatest risk and photoageing signs may be noticeable around the age of 40.

Some common signs of photoageing include: Coarse/ fine wrinkling, yellow discolouration of skin, scarring, erythema (superficial reddening of the skin, usually in patches) and telangiectasia (widening of the venules cause red lines/ patterns on the skin).

Why do we need to use sunscreen?

Sunscreens are able to block UVA, UVB and visible light. There are two types of sun screens.

Physical sunscreens contain titanium dioxide or zinc oxide and can reflect UV radiation. These are often more effective and protective against skin cancer. Physical sunscreens are often more thick and opaque but rub off more easily and must be frequently reapplied.

Chemical sunscreens absorb UV radiation. The sun protection factor (SPF) indicates the UVB photo protection in the sunscreen or in other words, is a measure of the fraction of sunburn producing UV rays that reach the skin.

How do you know which SPF to use?

If your skin is prone to burning after 10 minutes, applying SPF 15 would allow you to stay in the sun without burning for around 150 minutes. This is an estimate and usually depends on your skin type, the intensity of sunlight exposure and how much sun screen you apply. SPF 30 or higher is recommended for the majority of patients.

Dr S Mohsen KhorshidMD, FRCP, MSc, Dip RC Path

I am a Consultant Dermatologist and former Clinical Lead for Dermatology Services for South Essex, based at the Arthur Rook Centre for Dermatology, Basildon Hospital. I also work Barts Health NHS Trust as a Senior Lecturer in Dermatopathology since 1998. I started my specialist dermatology training at Shiraz University, Iran in 1990 and completed at The Royal Free Hospital, London in 1998. I also trained at St John’s Dermatology Centre, St Thomas’ Hospital, St Bartholomew’s Hospital and The Royal London Hospital.